Grid-type electronic tube

ABSTRACT

The present invention relates to electronic tubes with grids of cylindrical structure. In tubes of this kind, where the cathode and the grids take the form of highly cut away cylinders, the invention, in order to secure better mechanical stability on the part of the electrodes, provides for the cathode to be split, in the height sense, into several sections 1, 10, said sections being given different diameters, the grids, 8, exhibiting at the level of the spaces defined between said sections, non-cylindrical connecting surfaces 13 playing the part of stiffeners. Application to triodes for short wave transmitter applications (20 MHz).

United States Patent 1 1 3,930,179 Gerlach et al. Dec. 30, 1975 GRID-TYPE ELECTRONIC TUBE [75] Inventors: Pierre Gerlach; Roger li-lloet, both of Paris, France Primary Examiner-Alfred E. Smith Assistant ExaminerWm. H. Punter Attorney, Agent, or Firm-Roland Plottel [73] Assignee: Thomson-CSF, Paris, France [22] Filed: Dec. 17, 1974 [57] ABSTRACT 21 APPL 533,715 The present invention relates to electronic tubes with grids of cylindrical structure.

In tubes of this kind, where the cathode and the grids [3O] Forelgn Apphcatmn Pnomy Data take the form of highly cut away cylinders, the

Dec. 21, 1973 France 73.46038 invention, i order to Secure bett r me hanical stability on the part of the electrodes, provides for the [52] US. Cl. 313/296; 313/301 cathode to be Split in the height Sense into Several [51] Int. Cl. H01] 1/46; HOIJ 21/20 Sections 1 10 said Sections being given different [58] Field of Search 313/6 301 diameters, the grids, 8, exhibiting at the level of the spaces defined between said sections, non-cylindrical [56] References Cited connecting surfaces 13 playing the part of stiffeners.

UNITED STATES PATENTS Application to triodes for short wave transmitter 1,794,242 2/1931 Pelletier 313/301 applications (20 1,930,147 10/1933 Pirani 2,288,812 7 1942 Linder 313 301 1 Claim, 2 Drawing Flgures l"! l l I l 1 4 I! 2 U.S. Patent Dec. 30, 1975 Sheet 1 of2 3,930,179

US. Patent Dec. 30, 1975 Sheet 2 of2 3,930,179

GRID-TYPE ELECVITYIIONIC TUBE '1 The present invention relates to a grid type electronic tube in which the various electrodes, namely'thecathode, the grid or grids, and the anode, all cylindrical in form, are arranged about a common axis, the tube axis.

In tubes possessing this kind of structure, a structure encountered in particular in triodes for short wave transmitter application, the emissive section of the cathode is made of spaced wires. This applies to cathodes of the cage type, which consist of ame'tal mesh coiled cylinder fashion and attached tosupports; it is also the case with pin type cathodes, where the wires take the form of pins stretched between the two ends of the cylinder.

Whatever the precise shape which they take, these cathodes always, because of the wire structure, constitute light and highly cut away structures, vulnerable to mechanical vibrations which affect their stability. The seriousness of the problems posed by this stability can be appreciated by considering that in certain tubes, these cathodes have substantial dimensions, i.e. cylinder diameters of 120 millimetres and more, heights of 300 millimetres and operating temperatures, taking the most highly emissive materials, of the order of 1650 C.

The grids, in the case of a triode the single grid, are cylinders coaxial with the cathode and surrounding the latter, the first of them furthermore, for electronic reasons, having a diameter very little greater than that of the cathode. This grid too, like the cathode, has a highly cut away structure and a small thickness, both being essential conditions for the grid to present adequate transparency to the electron beam; the same applies to the other grids for the same reasons; these grids thus, ultimately, constitute light and highly cut away components which are extremely vulnerable to the effects of mechanical vibrations.

They may, furthermore, be metallic, like the cathode, or be made of graphite as in the more modern version of the tubes with which the invention is concerned. Whatever the material used to build the grids, they still face the problem of mechanical stability. This problem is the more serious since the distance between cathode and first grid is usually very short, as indicated aerlier, and since vibrations affecting these components may produce substantial variations in said distance, variations which may prejudice the proper operation of the tube. It must be added, too, that with cathodes operating at the temperature indicated earlier, said first grid is raised in operation to a temperature of 1250" C.

The object of the invention is an electronic tube of cylindrical structure, equipped with a cathode and grids having improved stability vis-a-vis vibrations, compared with that of similar prior art tubes.

In the tubes in accordance with the invention, the cathode is split into two or more parts in the direction of the tube axis. However, unlike the arrangement adopted in the prior art instances, these parts have mutually different diameters. In addition, the first grid, or the sole grid in the case of a triode, exhibits a change in diameter at the levels of the zones of separation between the different parts of the cathode, this in accordance with the conditions which will be specified hereinafter with reference to the two figures, in which:

FIG. 1 is a sectional view of a cathode-grid assembly of a prior art tube.

' bly modified in accordance with the invention.

- In the case of multi-grid tubes, the other grids likewise, in accordance with the invention, may exhibit the same form. The anode also exhibits this form.

FIG. 1 illustrates in section a cathode-grid assembly belonging to aprior art tube, in the example a triode. To simplify the drawing, theother electrodes of the tube have not been shown. The cathode surface shown at l is constituted by a mesh of metal wires wrapped cylinder fashion and, in operation, emitting a beam of electrons. The wires will for example be thoriumcoated tungsten. The cathode is finished by a base having the form of a disc, 2, and a ring, 3, both made of metal, to which the aforesaid cylinder is attached at its two ends. It is supported by two sets of rods, numbering three in each set, for example, only two of which have been shown in the sectionnal view of the figure, being marked there by the reference 4 and 5 attached at their bottom ends -to dished supports 6 and 7 respectively. These dished components, made of metal, serve to establish connections with the heating current genera tor which has not been shown.

The grid, marked 8, consists of a cylnder the internal dimension of which is very slightly larger than that of the metal mesh 1 as the drawing shows, the cathodegrid interval generally being of the order of 1 mm in this type of tube. The cylinder, made for example of graphite, terminates at one of its ends in a bottom 9 and is flared at its lower end where it is welded to a third dished component 11, an electrically conductive element, through which the grid bias voltage is applied; 12 illustrates insulating spacers.

The section shown in FIG. 2 illustrates the same assembly depicted by the preceding figure, this time modified in accordance with one embodiment of the invention which is given by way of a non-limitative example. There, again, there can be seen a cathode surface formed by a metal mesh wrapped to form a cylinder 1. However, whereas the preceding figure illustrated a cathode of onepiece form constituted by the mesh 1 and attached to the base 2 and to the ring 3, in the example in FIG. 2 two cathode sections can be seen, one of which, the top part, has been assigned the same references as in FIG. 1; the same references employed in FIG. 1 have been utilised again for the supports and the dished components associated with this first portion, as an inspection of the drawing will show. Here, however, the supports are reduced to a single series of three rods, 4, and to a single dished component 6, for reasons which will become apparent hereinafter.

The second portion, the bottom portion in the figure, which has a larger diameter than the first, is constituted by the mesh 10 terminating at its two ends in the rings 20 and 30; it is carried by the two sets of three rods 5 and 50 terminating at the respective dished components 7 and 70. In the example in the figure, the two portions are attached together by metal spacers distributed along the rings 3 and 20 to which they are attached; two of these spacers are visible at 40 in the section of the figure; they provide electrical contact between the two portions of the cathode, so that heating of the latter is effected across the dished components 6,7 and 70.

The grid 8, as before, takes the form of a cylinder flared at one of its ends and terminating in a bottom 9 at the other.

However, whereas in the prior art arrangement of FIG. 1, the cylinder has a constant diameter over its full height, here, in the cathode-grid assembly of the tubes in accordance with the invention, the cylinder is made up oftwo sections of different diameters, attached at the split level between the two cathode sections, by a non-cylindrical surface 13, frusto-conical in the present example. This kind of attachment, because of the stiffening which it introduces, reinforces the mechanical stability of the grid.

in addition, the splitting of the cathode into two sections of lower height than the one-piece item of the prior art, other things being equal increases the mechanical stability of the network of wires in each of said sections.

In the example described, the cathode was split into two sections. In other variant embodiments, likewise fallingwithin the scope of the invention, the number of these sections can be chosen greater than two and the diameters of the sections can all be different from one 4 another. In this case, the grid cylinder 8 may comprise several connecting surfaces such as the foregoing surface 13, for example one at each of the split levels between the different sections involved.

The invention is applicable not only to the case of triode tubes which other than the anode comprise only the cathode and a single grid, but also to multi-grid tubes comprising, in addition other grids.

We claim:

1. An electronic tube with cylindrical electrodes, comprising a cathode, one or more grids, and an anode, consisting of cylinders arranged around a common axis, characterised in that said cathode is constituted by at least two separate sections of different diameters; and in that at least the first of said grids, that is to say that which is closest to said cathode, is made up of cylindrical sections of different diameters connected together by a non-cylindrical surface at the level of the splits between said sections. 

1. An electronic tube with cylindrical electrodes, comprising a cathode, one or more grids, and an anode, consisting of cylinders arranged around a common axis, characterised in that said cathode is constituted by at least two separate sections of different diameters; and in that at least the first of said grids, that is to say that which is closest to said cathode, is made up of cylindrical sections of different diameters connected together by a non-cylindrical surface at the level of the splits between said sections. 